VITAMIN D for PN PAIN AND BONE INTEGRITY
WHAT IS VITAMIN D?
Vitamin D (or calciferol) is a fat-soluble vitamin that is naturally present in a few foods, added to others, and available as a dietary supplement. It is also be produced internally when ultraviolet (UV) rays from sunlight strike the skin and trigger vitamin D synthesis. However, when it is first ingested, it is biologically inactive and must undergo two chemical changes in the body for activation. The first stage takes place in the liver, where Vitamin D is converted to a (pre)hormone called “calcidiol”. The second stage occurs in the kidney, where the newly created calcidiol is converted to “calcitriol”, the active form of vitamin D. (2)
Vitamin D deficiency in both adults and children is associated with numerous general health issues, such as type 1 diabetes, hypertension, broken bones, falls, depression, and more. However, this article focuses on vitamin D as a possible treatment for neuropathic pain and bone integrity, in individuals with osteoporosis and diabetic peripheral neuropathy respectively. (5)
VITAMIN D and OSTEOPOROSIS
Osteoporosis is a disease that is characterized by low bone mass and deterioration of bone tissue, which can lead to increased risk of fracture. It is sometimes associated with diabetic and other neuropathies because as nerves deteriorate the surrounding muscles weaken resulting in a higher risk of falling and resulting fractures. Osteoporosis can also be associated with diabetic neuropathy and possibly others, making bone fractures an even higher risk.
Vitamin D helps increase the absorption of calcium, building stronger bones. It also improves the function of muscles, therefore, improving one’s balance and decreasing the likelihood of falls, leading to fractures. Therefore, it is recommended that those over 50 or younger adults at high risk (with osteoporosis, progressing neuropathy, several fractures, or conditions affecting vitamin D absorption) should receive 800-2,000 IU daily. Healthy adults between 19-50 years of age, require around 400-1,000 IU daily.
VITAMIN D and DIABETIC PERIPHERAL NEUROPATHY
Diabetic peripheral neuropathy (DPN) is a common complication of type 2 diabetes, affecting up to 50% of patients and often resulting in foot and muscle weakness, balance disturbance, and neuropathic pain. The pain from DPN, in fact from any neuropathy, can be severe and leads to depression, sleep disorders, and reduced quality of life. DPN involves both small and large nerve fibers. Small fibers (called C-fibers) are associated with electric shock or burning symptoms, while large fiber impairments affect balance. Vitamin D deficiency seems to be common in patients with type 2 diabetes, especially those with symptoms of DPN, and studies have shown that low levels may be an independent predictor of DPN development. In a randomized, placebo-controlled study of patients with DPN and low vitamin D levels, researchers examined the effects of replacement therapy on neuropathic pain and balance; this was the first investigation of vitamin D on balance disturbances in patients with DPN. Their study was based on research that showed vitamin D-associated improvements in axon regeneration and myelination following nerve injury, as well as increases in nerve growth factor (NGF) synthesis and prevention of neuronal degeneration. The axon is also called a nerve fiber and is a portion of a nerve cell (neuron) that carries nerve impulses away from the body. Myelin is the “insulation” that covers the axons, which speeds up the electrical impulses along the nerve cells. NGF is a protein necessary for the differentiation and maintenance of neurons. Therefore, previous research indicated that vitamin D could potentially recover damaged neurons, aid in myelin production, increase NGF synthesis and prevent deterioration of neurons. In their study, a one-time injection of 300,000 IU vitamin D was administered to patients with low levels of vitamin D who had polyneuropathy (peripheral neuropathy; multiple peripheral nerves damaged) that was confirmed with electromyography (EMG). Neuropathic pain and balance were first assessed at baseline and again after 12 weeks using a “Douleur Neuropathique” (DN4; patient questionnaire to assess pain) and the Berg Balance Scale (a functional balance test).
After 12 weeks, patients’ questionnaire scores reflected a significant decrease in neuropathic pain compared to baseline, and balance test scores were significantly improved (associated with large fibers). Patients showed a significant decrease in scores measuring electric shock and burning sensations (associated with small fibers) from baseline to the end of the study. The decrease in neuropathic pain indicates an improvement in small nerve fibers, and the improved balance test scores indicate an improvement in the large nerve fibers.
Although the neurotrophic effects of vitamin D on nerve function could be the primary reason for improvements in patients with DPN, other cellular factors, for example, may play a role by regulating the amount of activated vitamin D delivered to the muscle. It is also possible that vitamin D may elevate the pain threshold through a nociceptor (pain receptor) repair function. While research on this topic continues, vitamin D replacement therapy in addition to glucose-lowering diabetes treatment could address any deficiencies that may be causing neuropathic pain symptoms and balance impairment associated with DPN. This research is promising, and while it should be taken into consideration, it is also important to remember that many other factors can contribute to pain symptoms and balance impairment in individuals with DPN. (4,6)
- Osteoporosis website. “What is osteoporosis”.https://osteoporosis.ca/about-the-disease/what-is-osteoporosis/
- National Institutes of Health. “Vitamin D”. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
- Osteoporosis website. “Calcium and vitamin D”. https://osteoporosis.ca/bone-health-osteoporosis/calcium-and-vitamin-d/
- Christine Rhodes. “Vitamin D and Diabetic Peripheral Neuropathy”. https://www.practicalpainmanagement.com/painful-diabetic-neuropathy-vitamin-D
- Colleen E. Nadolski. “Vitamin D and Chronic Pain: Promising Correlates”. https://www.uspharmacist.com/article/vitamin-d-and-chronic-pain-promising-correlates
- S. Furukawa, Y. Furukawa. “Nerve growth factor synthesis and its regulatory mechanisms: an approach to therapeutic induction of nerve growth factor synthesis”. https://pubmed.ncbi.nlm.nih.gov/1980419/